This invention relates to lasers and more particularly to mirrorless, distributed-feedback lasers (DFB).
Resonance is achieved in a conventional waveguide laser by placing mirrors at the ends of the waveguide and adjusting their separation. Some disadvantages inherent in the use of mirrors are the difficulty of precise alignment and the necessity of periodic replacement. A distributed feedback laser (DFB) eliminates the need for end mirrors. A periodic perturbation within the waveguide produces Bragg scattering so that the incident and reflected waves reinforce each other and allow laser action in the absence of discrete mirrors. The degree to which the incident wave interacts with the periodic perturbation is described by the coupling constant, K. As K increases, laser action may occur at lower gains and/or shorter waveguide lengths.
Heretofore, the only means proposed for producing distributed feedback in a gas waveguide laser was to provide periodic corrugated surfaces along the length of the amplifying medium.
Since the incident wavefront only interacts with the perturbation along the walls of the waveguide, the coupling constant, K, is necessarily small. If the separation between the walls of the waveguide is decreased to increase K, the volume of the amplification medium will also be decreased thereby decreasing the output power of the laser.